EP0767331B1

EP0767331B1 - Method for controlling a valve and an electromagnetic valve

Info

Publication number: EP0767331B1
Application number: EP96113321A
Authority: EP
Inventors: Göran Cewers; Göran Skog
Original assignee: Siemens Elema AB
Current assignee: Siemens Elema AB
Priority date: 1995-10-04
Filing date: 1996-08-20
Publication date: 2002-04-03
Anticipated expiration: 2016-08-20
Also published as: SE9503437D0; US5787924A; DE69620332T2; EP0767331A1; DE69620332D1; JPH09126345A

Description

The present invention relates to a method for controlling a valve having a mechanically journalled movable means for regulating the opening of the valve, said movable means being journalled in a stationary bearing, and an electromagnetic valve whose degree of opening is adjustable with a means movable in a stationary mechanical bearing.

In valves, whose degree of opening can be regulated with a mechanically journalled movable means, friction in the bearing can cause problems. Friction is often unpredictable, since it changes with the age of the valve, the pressure of the movable means against the bearing etc., and friction often causes the movable element to "stick" in a particular position. This problem is obviously greatest in the regulation of small flows through the valve, a procedure which requires small, precise movements by the movable means. When larger flows are involved, an error in the degree of opening of the movable means is not as critical.

GB 2 173 283 describes such a valve in which the aforementioned undesirable effects caused by friction are eliminated. The valve is arranged with an actuator as the movable means which is slidably mounted on a support structure so as to be able to move along the support and thereby regulate the degree of opening of the valve. When the actuator is at a desired position the support is then oscillated back and forth along the actuator to prevent the actuator sticking to the support.

For valves in closed regulatory systems, the aforementioned undesirable effects caused by friction can, in principle, be eliminated by means of feedback regulation. EP-0 360 809 describes such a feedback valve device for exact regulation of an emitted flow to achieve a flow of the desired magnitude.

However, there are limits on the degree of amplification permissible in such feedback systems, i.e. in the size of the error signal representing the difference between the desired flow and the true flow, since the system becomes unstable when amplification is too great. These problems in feedback regulatory systems are discussed in CH, B2 430 837. This document also describes another device for damping oscillations in such a system by the addition of a special stabilization signal to the feedback error signal constituting the difference between the reference signal set and the actual signal.
The object of the present invention is to eliminate, or in any case reduce, the friction in a movable means used for regulating the opening of a valve.

This object is achieved with a method and a valve of the aforementioned kind with the features set forth in patent claims 1 and 7.

When the valve's movable means is made to move in relation to its bearing, friction is reduced to a low, well-defined value. This accordingly eliminates the aforementioned problems caused by friction, making precise regulation of even very small flows possible with the valve.

According to advantageous embodiments of the method according to the invention, the movable element and bearing are made to move back and forth in relation to each other, e.g. in an oscillating, rotary or translatory movement.

With a valve, whose degree of opening is varied through a translatory movement of the movable means (an example of this type of valve is described in US,A,5 265 594), the oscillating movement then occurs around the opening position of the movable means, the magnitude of oscillating movement here being so small that fluctuations, caused by variations in the valve's degree of opening, in the flow passing through the valve, are held within acceptable limits. A certain amount of fluctuation, or inaccuracy, in the set flow is normally acceptable, and inaccuracy in the flow caused by the said oscillating movement of the movable means, after damping in any connected tube, must lie within permissible limits.

According to another advantageous embodiment of the method according to the invention, the translatory movement amounts to one percent or less of the maximum translatory movement which is possible for varying the valve's degree of opening.

According to another advantageous embodiment of the method according to the invention, the movable means can be made to rotate in the bearing around its own axis of symmetry.

According to advantageous embodiments of the valve according to the invention, the movement device is arranged to be optionally connectable and disconnectable. It can e.g. be connected when an error signal, representative of the difference between the desired degree of valve opening and the true degree of valve opening, exceeds a predefined value, or it can be connected when the valve's degree of opening is less than a predefined value, i.e. when sufficiently small values are to be regulated. The movement device can also be advantageously arranged, so it is disconnected when there are large changes in the valve's opening, i.e. when there are large changes in the set flow. The movement device can also be arranged to be connected by the aforementioned error signal and be arranged to impart relative motion, whose magnitude varies with the magnitude of the error signal, to the movable means and bearing. This optional connection and disconnection capability for the movement device is advantageous, since the movement device is normally electrically powered and its operation therefore increases power consumption. The movement of the movable means in relation to its bearing can also cause disruptive acoustic effects. However, this disruption can be reduced if the movement device is only operated periodically.

According to other advantageous embodiments of the valve according to the invention, the movable means contains a valve body and/or driver means for positioning the valve body. The valve body can contain a membrane, devised to rebound away from a valve seat and the driver means, a rod, devised to push the membrane to a desired position in relation to the valve seat, overcoming the membrane's own resiliency. The rod can be made at least in part of, or be coated with a magnetic material, and arranged inside a coil, movable towards or away from the valve seat in order to position the rod and, accordingly, the membrane in relation to the valve seat by controlling the current applied to the coil. Here, the movement device superimposes a much smaller current on the current to the coil in order cause the rod and, accordingly, the membrane to move around the prevailing degree of opening. Alternately, the rod can be movable in the magnetic field from two opposed coaxial coils, the rod and, accordingly, the membrane being movable to a desired position in relation to the valve seat when current to the coils is controlled. Here, the movement device superimposes a much smaller current on the current to at least one of the coils in order to cause the rod and, accordingly, the membrane to move around the prevailing degree of opening.

According to yet another embodiment of the valve according to the invention, the superimposed current is sinusoidal and has a frequency in the 100 to 500 Hz range. The frequency is then less than the upper limit frequency of the electromagnet while simultaneously being high enough for oscillations, occurring in the gas flow caused by the movement induced by the superimposed current, to be filtered out in connected tubing.

The invention will now be described in greater detail, referring to the attached drawing which shows an exemplifying embodiment of the valve according to the invention.

The valve contains an inlet 2 whose opening 4 can be opened and closed with a membrane 6.

The membrane 6 is elastically resilient. To close the valve, the rod 8 pushes the membrane 6 against the opening 4. To open the valve, the rod 8 retracts, (upward in the FIG.), whereupon the membrane 6 rebounds resiliently away from the opening, so a flow can pass through the inlet 2, via the opening 4, out through the outlet 10. So the membrane 6 is devised to rebound resiliently away from the opening 4.

The rod 8 passes through the enclosure 12 and is journalled at 14 and 16 for movement in its longitudinal direction. The

bearings

14, 16 are made with close tolerances, since they serve as guides for the rod 8.

An anchor 18 made of magnetic material is arranged on the rod 8, and this anchor is movable inside a coil, so the anchor and, accordingly, the rod 8 can be moved back and forth in the rod's longitudinal direction when an appropriate current is applied to the coil 20.

Instead of having a separate anchor arranged on the rod, at least a part of the rod itself can be made of a magnetic material which serves as the anchor. Alternately, the rod can be at least coated with magnetic material.

For safety reasons, the rod 8 can be spring-loaded to press against the closed position (not shown), so the valve shuts as soon as the current I to the coil 20 is shut off.

Instead of having the spring-loaded rod press against the valve's closed position and opening the valve with an electromagnetic force which counteracts the resilient force, the rod can be positioned with opposing magnetic fields from two coaxial coils, the superimposed current then appropriately being applied to one of the coils.

The valve's degree of opening, i.e. the magnitude of the distance between the opening 4, serving as a valve seat, and the membrane 6 can also be adjusted by controlling the current I to the coil 20.

A position sensor 22 is advantageously arranged to sense the position of the valve and is connected to the current control means 24, so the current I to the coil 20 is regulated at values enabling the rod 8 and, accordingly, the membrane 6 to assume the desired position.

Friction in the

bearings

14, 16 often causes the rod to "stick". This friction is an unpredictable factor which e.g. changes with the age of the valve, the side of the rod 8 which presses against the bearing etc. When the error signal generated by the position sensor 22 achieves a sufficient magnitude, the current I to the coil 20 is increased, dislodging the coil and causing it to assume a new position. When large flows are regulated, the problems caused by friction are normally negligible, e.g. because errors in the rod's 8 and, accordingly, the membrane's 6 position are small in relation to the valve's total movement. However, when regulation of small flows is involved, friction in the bearings can cause serious problems.

So for that reason, a smaller current, preferably a sinusoidal signal, is superimposed on the current I, causing the rod 8 to oscillate around the valve's opening position, and, accordingly, the membrane 6, which is governed by the desired degree of valve opening. Since the rod 8 is accordingly kept in motion the whole time, in relation to the

bearings

14, 16, the rod is prevented from getting "stuck".

The frequency of the superimposed signal is lower than the upper limit frequency of the electromagnet but still high enough for oscillations in flow to be quickly filtered out in the valve tubing normally connected to the outlet 10. A suitable frequency is in the 100 to 500 Hz range.

The amplitude of the superimposed current must be so small that ensuing oscillations in flow always remain within permissible limits. So the amplitude of the superimposed current should advantageously be such that the magnitude of the ensuing movement is on the order of one percent or less of the maximum travel possible for varying the valve's degree of opening.

The superimposed current will increase the electromagnet's power consumption, so the current control means 24 is appropriately arranged to apply the superimposed current only when needed, e.g. when the error signal from the position sensor 22 becomes unacceptably large or, when a small reference signal is sent to the electromagnet, i.e. in the regulation of small flows. The disruptions which acoustic effects in the valve can cause when the superimposed current is applied are also reduced accordingly.

Moreover, disconnection of the superimposed current may be appropriate when major changes occur in flow through the valve, i.e. when there are major changes in the position of the rod.

The amplitude of the superimposed signal can be constant or, alternately, governed by the error signal or the reference signal.

One embodiment has been described above in which a oscillating, translatory movement is generated in a rod journalled in

bearings

14, 16 with the aid of a superimposed current in the coil 20 to keep the rod 8 from getting stuck in the

bearings

14, 16. Alternately, the valve can be devised so the rod, with the aid of the superimposed current, is made to rotate on its longitudinal axis around a mid- position, or the rod 8 can be continuously rotated around its longitudinal axis.

The membrane 6 is appropriately compressible, so the rod 8 is able to perform an oscillating, translatory movement even with the membrane 6 pressed against the valve seat 4. The membrane 6 will then be alternately compressed and expanded.

"Sticking" between the valve seat and the valve membrane 6, which can also contribute to the valve becoming "stuck" in the closed position, can also be reduced by imparting motion to the rod 8 as described above.

One embodiment was described above in which a valve membrane is positioned with a special electromagnetic driver device. Other types of valve bodies, directly positioned by an electromagnet, can obviously also be used.

Claims

A method for controlling a valve having a means (8) mechanically journalled in a stationary bearing (14;16) for movement to regulate a degree of opening of the valve, characterized in that in order to reduce the friction of the means (8) in the bearing (14;16) said means (8) is made to perform a friction reducing movement in an opening position determining a prevailing degree of opening of the valve.
A method according to claim 1, characterized in that said means (8) is made to perform a back and forth movement relative to the stationary bearing (14;16) as the friction reducing movement.
A method according to claim 2, characterized in that the back and forth movement is a rotation movement.
A method according to claim 2, the degree of opening of the valve being varied by translatory movement of the means (8), characterized in that the back and forth movement is a translatory movement around the opening position of a magnitude such that fluctuations in the flow passing through the valve, caused by ensuing variations in the degree of opening of the valve, remain within acceptable limits.
A method according to claim 4, characterized in that the translatory movement amounts to one percent or less of the maximum translatory movement which is possible for varying the degree of opening of the valve.
A method according to any of claims 1-3, said means (8) being rotation symmetrical, characterized in that the means (8) is made to rotate in the bearing (14;16) around its axis of symmetry as the friction reducing movement.
An electromagnetic valve comprising a valve opening (4); means (8) movable relative to the valve opening (4) to regulate a degree of opening of the valve; a stationary mechanical bearing (14;16) in which the means (8) is journalled for the movement relative to the valve opening (4); characterized in that a movement device (24) is arranged to cause the means (8) to perform a friction reducing movement in an opening position determining the prevailing degree of opening of the valve.
A valve according to claim 7, characterized in that the movement device (24) is arranged to cause the means (8) to perform a back and forth movement relative to the stationary bearing (14;16) as the friction reducing movement.
A valve according to claim 8, characterized in that the back and forth movement amounts to one percent or less of the maximum movement possible for the means (8) for varying the degree of opening of the valve.
A valve according to any of claims 7-9, characterized in that the movement device (24) is arranged for optional connection/disconnection.
A valve according to claim 10, said valve being a part of a feedback regulatory system, in which an error signal, representative of the difference between a desired degree of opening of the valve and a true degree of opening of the valve, is generated in order to move the means (8), on the basis of the error signal, towards the opening position corresponding to the desired degree of opening, characterized in that the movement device (24) is arranged to be connected when the error signal exceeds a predefined value.
A valve according to claim 10, the valve being a part of a feedback regulatory system, in which an error signal, representative of the difference between a desired degree of opening of the valve and a true degree of opening of the valve, is generated in order to move the means (8), on the basis of the error signal, towards the opening position corresponding to the desired degree of opening, characterized in that the movement device (24) is arranged to be connected by the error signal and to impart to the means (8) a movement, relative to the stationary bearing (14;16), whose magnitude varies with the magnitude of the error signal as the friction reducing movement.
A valve according to claim 10, characterized in that the movement device (24) is arranged to be connected when the degree of opening of the valve is less than a predefined value.
A valve according to claim 10, characterized in that the movement device (24) is arranged to be disconnected when major changes occur in the degree of opening of the valve.
A valve according to any of claims 7-14, characterized in that the means comprises a valve body (6) and a driver means (8) for positioning the valve body (6).
A valve according to claim 15, wherein said valve opening has a valve seat (4); said valve body comprises a membrane (6) having an inherent resiliency and devised to rebound away from the valve seat (4); and said driver means comprises a rod (8) made at least in part of or coated with a magnetic material (18) for pushing the membrane (6) to a desired opening position in relation to the valve seat (4) against the inherent resiliency of the membrane; and a coil (20) to which a controllable magnitude current may be applied and having the rod (8) arranged inside so as to be able to move away from or towards the valve seat (4) in order to position the membrane (6) in relation to the valve seat (4) by controlling the current characterized in that the movement device (24) is arranged to superimpose a much smaller current on the controllable current applied to the coil (20) in order to cause the rod (8) and, accordingly, the membrane (6) to move around a prevailing opening position as the friction reducing movement.
A valve according to claim 15, wherein said valve opening has a valve seat (4); said valve body comprises a membrane (6); and said driver means comprises a rod (8) being at least partially made of or coated with a magnetic material (18) for pushing the membrane (6) to a desired position as the opening positions relative to the valve seat (4); and two coils to which controllable currents can be applied and which are arranged to generate two opposing coaxial magnetic fields in which the rod (8) is disposed for movement towards or away from the valve seat (4) by controlling the current applied to the coils and so achieve the desired opening position, characterized in that the movement device (24) is arranged to superimpose a much smaller current on the controllable current applied to at least one of the coils in order to cause the rod (8) and, accordingly, the membrane (6) to move around a prevailing opening position as the friction reducing movement.
A valve according to claim 17, characterized in that the superimposed current is so small that the variations it causes in the degree of opening of the valve produce fluctuations within acceptable limits in the flow passing through the valve.
The valve according to any of the claims 16-18, characterized in that the superimposed current is sinusoidal and has a frequency in the 100-500 Hz range.